Displays devices typically display data from a single source at a time that is presented to the display through a hardware interface video cable. When a display is configured to display data from more than one source, video switching systems can be used that take more than one video interface cable as input and produce an appropriate video signal to the display. In either case, the mapping from video sources to video displays is defined by the physical hardware connections between them. A traditional display system involves two primary components—an image generator and a display, connected via a video cable. The image generator is responsible for generating a video stream that is then presented by the display device. Examples of image generators include DVD players, Personal Computers, etc.
The image generator is not responsible for directing its output to a particular display—this is accomplished through the physical connection from the output video signal to the input of the display where the image is to be shown. In cases when a video cable is not used, other one-to-one video transport standards are used to define this output to display mapping. These standards act as different transport mechanisms for the video data, but still rely on a one-to-one mapping between display and content source. Even in cases where multiple sources are aggregated onto a single display output device, image generators are physically connected to hardware that then explicitly defines the image generator-to-display mapping. Examples of image aggregation hardware of this type include video wall controllers, video switchers, and scalars. Although device-specific data can be exchanged in this model—for example the EDID (Extended Display Identification Data) protocol allows the display to describe its properties (resolution, scan rate) to the image generator—this mechanism still requires a pre-determined physical connection between the image generator and display itself. An arbitrary image generator is unable, for example, to dynamically map its output to an arbitrary display device.